Method and Controller for Identifying a Unit in a Solid State Memory Device for Writing Data to

Abstract

In a method for identifying a unit in a solid state memory device for writing data to a tier structure is maintained the tier structure comprising at least two tiers for assigning units available for writing data to. In response to receiving a request for writing data it is determined if a unit for writing data to is available in a first tier of the at least two tiers. In response to determining that a unit is available for writing data to in the first tier this unit is identified for writing data to, and in response to determining that no unit is available for writing the data to in the first tier it is determined if a unit is available for writing data to in a second tier of the at least two tiers subject to a priority of the write request.

1 . A method for identifying a unit in a solid state memory device for writing data to, comprising:
 maintaining a tier structure comprising at least two tiers for assigning units available for writing data to;   in response to receiving a write request, determining if a unit for writing data to is available in a first tier of the at least two tiers;   in response to determining that a unit is available for writing data to in the first tier, identifying this unit for writing the data to; and   in response to determining that no unit is available for writing data to in the first tier, determining if a unit is available for writing data to in a second tier of the at least two tiers subject to a priority of the write request.   
     
     
         2 . The method of  claim 1 , further comprising:
 wherein in response to determining that no unit is available for writing data to in the first tier, determining if a unit for writing data to is available in the second tier if the write request is of a first priority.   
     
     
         3 . The method of  claim 2 , wherein the write request is of a first priority if the write request is for relocating data stored in any one of the units of the solid state memory device. 
     
     
         4 . The method of  claim 2 , further comprising
 wherein in response to determining that no unit is available for writing data to in the first tier, blocking the write request if the write request is of a priority lower than the first priority.   
     
     
         5 . The method of  claim 4 , further comprising:
 wherein in response to determining that a new unit is available for writing data to in the first tier, unlocking the write request.   
     
     
         6 . The method of  claim 4 , wherein the write request is of a priority lower than the first priority if the write request is for writing data from a host external to the solid state memory device. 
     
     
         7 . The method of  claim 2 , wherein the tier structure comprises three tiers for assigning units available for writing data to. 
     
     
         8 . The method of  claim 7 , further comprising:
 wherein in response to determining that no unit is available for writing data to in the second tier, identifying a unit available for writing the data to in a third tier of the three tiers.   
     
     
         9 . The method of  claim 1 , wherein the units assigned to a common tier are arranged in at least one block, the method further comprising:
 maintaining a block in a tier as long as the block contains at least one unit available for writing data to, otherwise transferring the block to a pool of occupied blocks.   
     
     
         10 . The method of  claim 9 , further comprising:
 wherein in response to transferring a block from a given one of the tiers to the pool of occupied blocks, determining if a free block is available;   if a free block is available, transferring a block assigned to a tier next lower than the given tier from which the block is transferred to the pool of occupied blocks to the given tier;   transferring blocks from a lower to a next higher tier for all remaining lower tiers; and   assigning the free block to a lowest tier of the tier structure.   
     
     
         11 . The method of  claim 9 , further comprising:
 determining if a free block is available from one or more of a free block pool and a block reclaiming process.   
     
     
         12 . The method of  claim 9 , further comprising:
 maintaining an index for identifying a next unit for writing data to within the tiers available, wherein the next unit is a unit of a highest tier amongst the tiers containing units available for writing data to; and   if the next unit is a last unit available for writing data to in the highest tier, advancing the index to a unit available for writing data to in a next lower tier as a new next unit after writing the data to the next unit.   
     
     
         13 . The method of  claim 1 , further comprising:
 maintaining wherein a tier structure comprising at least two tiers for assigning units available for writing data for each of multiple dies of the solid state memory device;   maintaining an index for identifying a next unit for writing data to within the tiers available for each of the multiple dies; and   selecting a die out of the multiple dies for writing data to.   
     
     
         14 - 23 . (canceled)